1. Field of the Invention
The present invention relates to a method for sintering a magnetic core, and more specifically relates to a method for sintering a flattened tubular magnetic core which is for use as a noise suppressing component.
2. Description of the Related Art
A conventional noise suppressing component includes a flattened tubular magnetic core as shown in FIG. 10. High frequency noise propagating in a signal line is suppressed by the magnetic core 21 in an arrangement in which a signal line, such as a flat cable, is inserted through a slot-like through hole 22. Cores having a longer side dimension L of 10 mm to 100 mm and a shorter side dimension T of 1 mm to 10 mm, and a through hole 22 having shorter side dimension t of 0.3 mm to 8 mm in lateral cross-section are used commonly as the magnetic core 21. Conventional methods for sintering such a magnetic core 21 are shown in FIG. 11 and FIG. 12.
That is, the sintering method shown in FIG. 11 is a method of sintering flattened tubular compacts 21 having a through hole 22, made of a ferrite material, while the flattened tubular compacts 21 are upright on the opening surface of one end in a sintering container (not illustrated) such that an axial direction of the compact 21 is vertical. Furthermore, the sintering method shown in FIG. 12 is a sintering method with flattened tubular compacts 21 arranged in a sintering container (not shown) such that the axial direction thereof is horizontal.
However, conventional sintering methods for magnetic cores cause problems in that since amounts of friction are large at the contacting surfaces of the flattened tubular compacts 21 and the sintering container, the flattened tubular compacts after sintering (that is, the magnetic cores) 21 can be severely deformed. Moreover, chemical reactions with the sintering container can easily occur so that discoloration or chipping due to adhesion to the sintering container may occur. In order to prevent this from occurring, the flattened tubular compacts 21 are sometimes sintered on highly pure alumina powder or zirconia powder spread in the sintering containers.
However, when the flattened tubular compacts 21 are sintered while upright in the sintering container as shown in FIG. 11, a problem arises in that the flattened tubular compacts 21 may become tilted and deformed, or adjacent flattened tubular compacts 21 may come into contact with each other, generating reactions, adhesion, or chipping due to small vibrations or shocks during transport.
In contrast, when the flattened tubular compacts 21 are baked while being arranged on their sides in the sintering container with the axial directions thereof disposed horizontally, as shown in FIG. 12, the problems of skewing or contact generated when the flattened tubular compacts 21 are sintered upright can be solved. However, when the flattened tubular compacts 21 soften during sintering, the side wall portions at the upper sides of the laterally oriented compacts 21 may sag toward the through hole 22 side. Therefore, another problem arises in that the shorter side dimension t of the through hole 22 of the flattened tubular compacts after sintering (the magnetic cores) 21 may be less than the desired value.
In order to solve the problems with conventional methods as described above, preferred embodiments of the present invention provide a method for easily sintering a magnetic core easily while preventing damage to the core caused by sagging or deformation.
According to one preferred embodiment of the present invention, a method for sintering a magnetic core includes the steps of providing a flattened tubular compact made from a magnetic material and having a through hole, providing a supporting plate which is constructed to maintain its shape at a sintering temperature of the flattened tubular compact, inserting the supporting plate through the through hole of the flattened tubular compact, and sintering the flattened tubular compact while the supporting plate is located in the through hole of the flattened tubular compact.
The supporting plate may be made of, for example, a sintered ceramic material or a metal material.
Since the flattened tubular compact is sintered with the supporting plate inserted through the through hole thereof, even when the flattened tubular compact softens during sintering, producing the possibility of xe2x80x9csaggingxe2x80x9d, the shorter side dimension of the through hole of the magnetic core is not be less than the thickness dimension of the supporting plate.
Furthermore, since the supporting plate is preferably tapered in the direction of insertion into the through hole of the flattened tubular compact, the operation of removing the supporting plate from the flattened tubular compact after sintering (the magnetic core) is greatly facilitated.